Reaching people by phone in Boston was difficult Monday following the explosions, but text messages could get through. Many athletes checked in on Twitter and Facebook.

The University of Colorado's athletic department said in a tweet that former Buff runner Kara Goucher was safe.

"My heart is broken, but my family and I are fine," Goucher, who now lives in Duluth, Minn., tweeted later in the day. "Please pray for those who aren't."

Bill Sullivan, the father of Sara Sullivan, a 2006 Longmont High School graduate who completed the marathon, said his daughter was safe, but was close enough at the time of the explosion that she had to take cover with her boyfriend.

"She's fine, but there are a lot of people out there hurting right now," Bill Sullivan said.

Fernando Cabada, a Boulder-based distance runner who is a three-time national champion in the 25-kilometer event, posted on Facebook that he and his mother, Magdalena "Vicki" Cabada, were safe but under lockdown in their hotel, which is 200 to 300 meters from the explosion.

"Very tragic," he wrote. "Keep Boston in your prayers."

Susan Kohuth said the atmosphere two blocks away in the family waiting area was relatively calm, with many people initially unsure what exactly they had heard. Within 10 minutes, law enforcement and emergency responders were streaming into the area, she said. It took about 30 minutes to confirm there had been explosions and that people were hurt.

The Kohuths' two daughters, ages 9 and 14, were with Susan Kohuth at the 26-mile marker watching the race, but it was too crowded near the finish line and they went to the family waiting area after seeing Steve Kohuth run past.

Kohuth, a counselor at Denver East High School, started running in marathons about six years ago. The Boston Marathon was his third.

Susan Kohuth said the "what-ifs" are starting to go through her mind, and her thoughts and prayers are with the injured and killed and their families.

She also praised emergency responders.

"Even before this happened, we were impressed with the Boston police," she said. "After, they were doing a great job getting the ER vehicles in and people moving out as we left."